This invention relates to a method and device for press-forming a topless hat-shaped hollow article having a flange as shown in FIG. 1 in one step by utilizing a method of forming a planar material by plastic deformation.
There are a great variety of hollow articles having flanges at their ends, such as hollow hat-shaped bodies such as gear blanks b as shown in FIG. 1. A convential method for producing these articles is shown in FIGS. 2(I)-2(IV).
The conventional method shown in FIG. 2 for producing a topless hat-shaped hollow article having a through hole internally comprises cropping a bar material into a blank d as shown in FIG. 2(I), smoothing both ends thereof and providing the blank with a tapered surfaces e as shown in FIG. 2(II), forming a hat-shaped blank by swaging a flange part f as shown in FIG. 2(III), and forming the outside of a hollow part g and the internal hole h therein as shown in FIG. 2(IV) by forcing a mandrel into the hole h and then piercing said mandrel through the top part of the product thereby to form the article (b) such as shown in FIG. 1. In this case, formation of the top hole of the product may be carried out together with the step for forming the hole h in FIG. 2(IV). This method requires not only four steps of operation, inclusive of one for material cropping into a blank, but also a great force in piercing the mandrel into the blank for press-forming the hollow part g. This force is applied through an area not wider than the cross-sectional area of the mandrel, thus entailing disadvantageous features such as buckling of the mandrel and shortening of the operational life of the same. Although there are methods for drilling and shaping the internal bore, these methods are not suitable for quantity or mass production and for reasons of economy.